/*
 * Copyright 2015 GenerallyCloud.com
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.tio.websocket.common.util;

public class BASE64Util {

	/**
	 * This array is a lookup table that translates 6-bit positive integer
	 * index values into their "Base64 Alphabet" equivalents as specified in
	 * Table 1 of RFC 2045.
	 */
	private static final char intToBase64[] = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z',
	        'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6',
	        '7', '8', '9', '+', '/' };

	/**
	 * This array is a lookup table that translates 6-bit positive integer
	 * index values into their "Alternate Base64 Alphabet" equivalents. This is
	 * NOT the real Base64 Alphabet as per in Table 1 of RFC 2045. This
	 * alternate alphabet does not use the capital letters. It is designed for
	 * use in environments where "case folding" occurs.
	 */
	private static final char intToAltBase64[] = { '!', '"', '#', '$', '%', '&', '\'', '(', ')', ',', '-', '.', ':', ';', '<', '>', '@', '[', ']', '^', '`', '_', '{', '|', '}',
	        '~', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5',
	        '6', '7', '8', '9', '+', '?' };

	/**
	 * This array is a lookup table that translates unicode characters drawn
	 * from the "Base64 Alphabet" (as specified in Table 1 of RFC 2045) into
	 * their 6-bit positive integer equivalents. Characters that are not in the
	 * Base64 alphabet but fall within the bounds of the array are translated
	 * to -1.
	 */
	private static final byte base64ToInt[] = { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
	        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 62, -1, -1, -1, 63, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -1, -1, -1, -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11,
	        12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, -1, -1, -1, -1, -1, -1, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47,
	        48, 49, 50, 51 };

	/**
	 * This array is the analogue of base64ToInt, but for the nonstandard
	 * variant that avoids the use of uppercase alphabetic characters.
	 */
	private static final byte altBase64ToInt[] = { -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
	        -1, 0, 1, 2, 3, 4, 5, 6, 7, 8, -1, 62, 9, 10, 11, -1, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 12, 13, 14, -1, 15, 63, 16, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
	        -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, 17, -1, 18, 19, 21, 20, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46,
	        47, 48, 49, 50, 51, 22, 23, 24, 25 };

	/**
	 * Translates the specified "alternate representation" Base64 string into a
	 * byte array.
	 */
	public static byte[] altBase64ToByteArray(String s) {
		return base64ToByteArray(s, true);
	}

	/**
	 * Translates the specified Base64 string (as per Preferences.get(byte[]))
	 * into a byte array.
	 */
	public static byte[] base64ToByteArray(String s) {
		return base64ToByteArray(s, false);
	}

	private static byte[] base64ToByteArray(String s, boolean alternate) {
		byte[] alphaToInt = alternate ? altBase64ToInt : base64ToInt;
		int sLen = s.length();
		int numGroups = sLen / 4;
		if (4 * numGroups != sLen) {
			throw new IllegalArgumentException("String length must be a multiple of four. len=" + sLen);
		}
		int missingBytesInLastGroup = 0;
		int numFullGroups = numGroups;
		if (sLen != 0) {
			if (s.charAt(sLen - 1) == '=') {
				missingBytesInLastGroup++;
				numFullGroups--;
			}
			if (s.charAt(sLen - 2) == '=') {
				missingBytesInLastGroup++;
			}
		}
		byte[] result = new byte[3 * numGroups - missingBytesInLastGroup];

		// Translate all full groups from base64 to byte array elements
		int inCursor = 0, outCursor = 0;
		for (int i = 0; i < numFullGroups; i++) {
			int ch0 = base64toInt(s.charAt(inCursor++), alphaToInt);
			int ch1 = base64toInt(s.charAt(inCursor++), alphaToInt);
			int ch2 = base64toInt(s.charAt(inCursor++), alphaToInt);
			int ch3 = base64toInt(s.charAt(inCursor++), alphaToInt);
			result[outCursor++] = (byte) (ch0 << 2 | ch1 >> 4);
			result[outCursor++] = (byte) (ch1 << 4 | ch2 >> 2);
			result[outCursor++] = (byte) (ch2 << 6 | ch3);
		}

		// Translate partial group, if present
		if (missingBytesInLastGroup != 0) {
			int ch0 = base64toInt(s.charAt(inCursor++), alphaToInt);
			int ch1 = base64toInt(s.charAt(inCursor++), alphaToInt);
			result[outCursor++] = (byte) (ch0 << 2 | ch1 >> 4);

			if (missingBytesInLastGroup == 1) {
				int ch2 = base64toInt(s.charAt(inCursor++), alphaToInt);
				result[outCursor++] = (byte) (ch1 << 4 | ch2 >> 2);
			}
		}
		// assert inCursor == s.length()-missingBytesInLastGroup;
		// assert outCursor == result.length;
		return result;
	}

	/**
	 * Translates the specified character, which is assumed to be in the
	 * "Base 64 Alphabet" into its equivalent 6-bit positive integer.
	 *
	 * @throw IllegalArgumentException or ArrayOutOfBoundsException if c is not
	 *        in the Base64 Alphabet.
	 */
	private static int base64toInt(char c, byte[] alphaToInt) {
		int result = alphaToInt[c];
		if (result < 0) {
			throw new IllegalArgumentException("Illegal character " + c);
		}
		return result;
	}

	/**
	 * Translates the specified byte array into an "alternate representation"
	 * Base64 string. This non-standard variant uses an alphabet that does not
	 * contain the uppercase alphabetic characters, which makes it suitable for
	 * use in situations where case-folding occurs.
	 */
	public static String byteArrayToAltBase64(byte[] a) {
		return byteArrayToBase64(a, true);
	}

	/**
	 * Translates the specified byte array into a Base64 string as per
	 * Preferences.put(byte[]).
	 */
	public static String byteArrayToBase64(byte[] a) {
		return byteArrayToBase64(a, false);
	}

	private static String byteArrayToBase64(byte[] a, boolean alternate) {
		int aLen = a.length;
		int numFullGroups = aLen / 3;
		int numBytesInPartialGroup = aLen - 3 * numFullGroups;
		int resultLen = 4 * ((aLen + 2) / 3);
		StringBuilder result = new StringBuilder(resultLen);
		char[] intToAlpha = alternate ? intToAltBase64 : intToBase64;

		// Translate all full groups from byte array elements to Base64
		int inCursor = 0;
		for (int i = 0; i < numFullGroups; i++) {
			int byte0 = a[inCursor++] & 0xff;
			int byte1 = a[inCursor++] & 0xff;
			int byte2 = a[inCursor++] & 0xff;
			result.append(intToAlpha[byte0 >> 2]);
			result.append(intToAlpha[byte0 << 4 & 0x3f | byte1 >> 4]);
			result.append(intToAlpha[byte1 << 2 & 0x3f | byte2 >> 6]);
			result.append(intToAlpha[byte2 & 0x3f]);
		}

		// Translate partial group if present
		if (numBytesInPartialGroup != 0) {
			int byte0 = a[inCursor++] & 0xff;
			result.append(intToAlpha[byte0 >> 2]);
			if (numBytesInPartialGroup == 1) {
				result.append(intToAlpha[byte0 << 4 & 0x3f]);
				result.append("==");
			} else {
				// assert numBytesInPartialGroup == 2;
				int byte1 = a[inCursor++] & 0xff;
				result.append(intToAlpha[byte0 << 4 & 0x3f | byte1 >> 4]);
				result.append(intToAlpha[byte1 << 2 & 0x3f]);
				result.append('=');
			}
		}
		// assert inCursor == a.length;
		// assert result.length() == resultLen;
		return result.toString();
	}

}
